I contemplated giving this bird to you as the daily Mystery Bird, but decided that you’d all probably riot, so instead, I am going to identify this bird so we can discuss it. It’s a House Sparrow, Passer domesticus. (I have received dozens of emails telling me I’m a dumbshit: this is clearly a Eurasian Tree Sparrow, Passer montanus, thus, my wavering ID).
House Sparrows were introduced in various places around the world where they have become established. Because House Sparrows are invasive species, are poor singers and are small, plain and dirty-brown in color, they are generally widely hated.

So let’s pretend that you were sitting at your breakfast table, sipping coffee while looking at your bird feeder, watching a flock of house sparrows pigging out, as usual. And let’s pretend that you suddenly noticed that one member of the flock was blue! What would you do?

Fortunately for us, this happened to Richard Shears, who grabbed his camera and photographed the bird above. That bird recently appeared at Shears’ bird feeder in Sydney, Australia with a flock of its normally colored companions. Shears managed to snap several photographs and, as you can see from the above image, this bird, which is probably a young male, is not dyed or otherwise painted in any way, nor is the image photoshopped.

So far, the experts are amazed by this bird’s color, but no one has, to the best of my knowledge, offered an explanation for it.

How did this bird develop blue plumage? Since blue pigments have so far proven elusive for birds to manufacture themselves, we know it isn’t the result of the bird suddenly being able to create it naturally. But blue birds exist, so how do they become blue? I wrote a piece about schemochromes — structural plumage colors — that will provide you with an in-depth look at blue feather color. In short, feathers create blue color by refracting light — it’s a physics trick that results in the feathers creating the appearance of being blue because they reflect blue light into the viewer’s eyes.

My hypothesis: this bird developed a mutation in one or more of the genes that govern the structural development of its feathers. This change caused the feather structure to be altered so it reflects blue light, thereby making the bird appear blue — which is true for all blue birds. I am not sure if anyone knows precisely how many genes need to be altered to produce blue feather color, but based on the sudden appearance of this blue bird, I’d guess that it’s only one or perhaps just a few, at most.

But now that blue color exists in this species, this raises all sorts of interesting possibilities. Will females suddenly prefer to mate with blue-colored males over normally-colored males, now that they have the choice of blue plumage color? How will this color mutation affect the social, behavioral and evolutionary dynamics of this sparrow population in Australia?

What is your hypothesis about the origin of this bird’s blue color? What do you think might happen with regards to the evolution of the species in Australia?

This is, as you say, pretty fascinating … but please be nice to House Sparrows – not everyone hates them and you just have to admire their ability to survive and adapt. After all the flashy, beautiful birds on the planet the House Sparrow is still the one that I’d miss the most if they went extinct. No question.

Interesting theory except that the bird appears to be a Eurasian Tree Sparrow (Passer montanus), not a House Sparrow. Tree Sparrow is introduced in Victoria and NSW, but is not regular in Sydney. This bird is probably an escape that is the result of some genetic experiment.

Surely only a minority of adults reproduce successfully. Otherwise we would be up to our navels in House Sparrows. So maybe it is too early to say that “blue” exists in HS. But I also share a soft spot for them. I hated them when they seemed to have driven House Finches out of Los Angeles, but 20 years ago or so I saw that HF was making a comeback, and now they compete aggressively with HS. Besides, twice I saw HS taking dust baths while ignoring people in close proximity–once in Venice, Italy, and once at the La Brea Tar Pits.

Perhaps a form of albinism? The blue doesn’t show up on the breast feathers, which would seem to count against a change in feather structure. Perhaps the bird’s normal coloration is a result of a combination of pigments, one of them became defective, and the other(s) make blue.

Off topic: Once at a job interview, the dean I was interviewing with (for an Asst. Professor of English position) asked me to tell him something about myself that was not on my CV. Since I am from St. Louis, I could tell him that I had seen a Eurasian Tree Sparrow. He stared at me and sort of blinked. I said, “Believe me, in the right circles there are people who would be very impressed.”

I can’t see the picture, but I suspect that dreikin is correct that it is some type of albino. In humans it is the absence of pigment that produces blue eyes. The blue is from scattering which preferentially occurs at shorter wavelengths. A mutation that produced a blue pigment and the absence of the normal brown pigment simultaneously would be pretty rare.

Many birds can see into the ultraviolet, so what birds look like to us may not be what they look like to each other. I think that some of them can even detect the polarization of light too.

That is truly amazing!! I saw some type of blue birds in my back yard last year at this time, and was trying to figure out what they were. I think they may have been a kind of indigo bunting, but not sure. But, possibly bluebirds. I live in Sioux Falls SD.

Could it possibly be a hybrid? House sparrows have hybridized with not even closely related passerines like Java Sparrows – perhaps a lone Tree Sparrow might hybridize with a local estrildine finch- some of those have blue or green in the plumage.

I think there is no doubt that this is a House Sparrow, Passer domesticus- if one takes a look at what I believe to be the same bird, one can see the dark lores and remnants of a chestnut nape which point to that species (in the photo above I can understand how some might have assumed the dark shadow to be a cheek spot but if you study the angle of the head, indicated by the direction of the bill, the dark patch is clearly behind where the cheek would be and therefore actually located on the nape, not the cheek).

Grrl’s point concerning the structural basis for “blue” feathering as opposed to non-turaco pigments covering the rest of the spectrum is important.

Unless the bird has developed this coloration through some form of structural mutation or through hybridization with a species carrying “blueness”, pigmentation disruptions or mutations similar to the Ino gene effect in budgerigars would not cause blue (as wild budgies are green- chemical yellow over structural blue- mutations within that species could prodce blue because it already posses the structural properties that apear blue) and similarly, although others on blogs about this bird have suggested carotenoid ingestation, there is no chemical basis that we know of yet that would produce blue.

It is important also to note that although white budgies that may have a bluish tinge to certain areas are called Albino, albinism, or even some form of leucism, could not in itself somehow produce blue- piebaldedness, patchiness, partial pigmentation, etc. only disrupt what pigmentation is already there, not somehow introduce one never present.

So we are back to two lines of inquiry- was the blue artificially introduced (paint, dye, etc.) or was it inherited through hybridization or somehow developed as a structural mutation?

re.23: I think blue mutations in any of the green parrots (mostly Psittacidae) are possible, again because of the inherent blue structural composition of the feathers combined with carotenoid yellow pigmentation- any disruption to the yellow will change green to blue…

re. 24: thanks for the aside- that cockatiels are in fact cockatoos (Cacatuidae) seems to have paved the way for this hybrid (apparently all three birds- the parents are bonded, are now up for sale!)… the article claims that no one had been able to cross cross-breed cockatiels with any other species before yet I have found records from the North West Bird Club in Tasmania that document hybridization with the Red Rumped Parrot (Psephotus haematonotus), Blue-winged Parrot (Neophema chrysostoma), and Eastern Rosella (Platycercus eximius) but since these would be all be interfamilial hybrids (the three listed above are from the family Psittacidae), I’m not convinced…

hmmm, still puzzling over the blue sparrow… my continued thoughts are that this is very likely not a hybrid with another “blue” species as I would expect other morphhological characteristics to be present and all I see is the sparrow- I’m not familiar with Australian birds, but of the blue ones that come to mind (for the Sydney area), it seems unlikely that hybridization with any of the Fairywrens (Malurus), blue mutations of any of the parrots, something like the Blue-winged Kookaburra (Dacelo leachii), or even species with grey-blue coloration like Silvereyes (Zosterops lateralis) would be possible or even viable.

There does exist the possibility that a blue form of a normally non-blue colored bird could develop as in the case of the Blue Chaffinch (Fringilla teydea), originally the Chaffinch (Fringilla coelebs) that developed blue coloration (still structutral) with successive colonizations of Tenerife and Gran Canaria, but the “original” already had the genetic wherewithall to produce blue, having a blue crown.

That this sparrow has been seen to flock with normal sparrows would seem to rule out general diet and reduces my quizzling to either an artificial cause (the most likely, and which includes a one-time ingestion of an artificial source) or a disease of the feathers (virus, cysts, barb cell mutation) that would cause a structural abnormality.